Case Western Reserve Student Puts Gorillas on a Diet

Free from poachers and sheltered from disease, zoo animals may seem to live rather cushy lives. However, two gorillas at the Cleveland Metroparks Zoo recently learned that staying healthy in captivity takes sacrifice.

Male gorillas in the wild weigh about 350 pounds, while the gorillas in question-Mokolo and Bebac-topped out at 460 and 430 pounds respectively.

"Heart disease—which, we know, is closely related to obesity in humans—is the leading cause of death for male gorillas in captivity," says Case Western Reserve University biology PhD candidate Elena Less. "We're trying to maintain as healthy a population of gorillas as we can."

To that end, Less initiated a diet program that is being tested in Cleveland and at four other zoos. She says it closely mirrors the eating habits of gorillas in the wild. The regimen is loaded with green vegetables like romaine lettuce, endive, dandelion greens and alfalfa hay. Gone are high-starch foods like carrots and bananas, and the animals' biscuits—the gorilla version of energy bars, which are rich in minerals but also high in sugar and calories—have been replaced by sugar-free gummy vitamins and other supplements.

The biscuit-free diet consists of almost five times more food-enough that zookeepers ditched the buckets they had used to transport the feed and switched instead to wheelbarrows-but it's high in fiber, low in sugar and starch and it forces the gorillas to work a little for their meals. They have to strip leaves and bark from sticks and roam around to track down pieces of hay, which takes more effort than simply popping a biscuit.

The extra effort has paid off. In the year since the diet change, Mokolo and Bebac each have shed about 65 pounds.

Less and her adviser, Kristen Lukas, PhD, a Case Western Reserve primatologist and a conservation expert at the zoo, say the apes took the change in stride.

"They resisted a little at first, but they've adapted well," Less says. "We used to give them biscuits for doing simple behaviors like getting on the scale, but we weren't giving them enough credit. They don't need a sugary reward; they'll do it for green beans."